There is a need for markers of infection status of an individual. Use of such markers allows treatment, prevention and control of the relevant disease. For example, monitoring the status of an individual infected with tuberculosis (TB) is essential for the treatment, prevention and control of this resurgent disease. Mycobacterial load cannot be measured directly and there is currently no biomarker reflecting mycobacterial load. In addition, Mycobacterium tuberculosis is often difficult to culture from patients with active TB, and impossible to culture from healthy latently infected people. Therefore an immune-based diagnostic test indicating the status of the Mycobacterium tuberculosis infection would be very useful in a number of clinical scenarios guiding the treatment, prevention and control of this infection. For example, differentiating between active and latent infection, monitoring efficacy of anti-tuberculosis therapy of active and latent TB, monitoring efficacy of therapeutic vaccines and new drugs and detecting early progression to active disease.
Mycobacterial antigens are known in the art. For example, early secretory antigen target-6 (ESAT-6) and culture filtrate protein 10 (CFP-10) are two Mycobacterium tuberculosis antigens that have been intensively investigated in animal models and humans over the last few years. ESAT-6 and CFP-10 are strong targets of 25 the cellular immune response in animal models, tuberculosis patients and contacts and so may be used in specific T cell-based blood tests.